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src/Control/Applicative/Local.hs

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+{- This file is part of Vervis.
+ -
+ - Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
+ -
+ - ♡ Copying is an act of love. Please copy, reuse and share.
+ -
+ - The author(s) have dedicated all copyright and related and neighboring
+ - rights to this software to the public domain worldwide. This software is
+ - distributed without any warranty.
+ -
+ - You should have received a copy of the CC0 Public Domain Dedication along
+ - with this software. If not, see
+ - <http://creativecommons.org/publicdomain/zero/1.0/>.
+ -}
+
+module Control.Applicative.Local
+    ( atMost
+    , atMost_
+    , upTo
+    , upTo_
+    )
+where
+
+import Prelude
+
+import Control.Applicative
+
+-- | Apply action between zero and @n@ times, inclusive, and list the results.
+atMost :: Alternative f => Int -> f a -> f [a]
+atMost n action = go n
+    where
+    go n =
+        if n <= 0
+            then pure []
+            else liftA2 (:) action (go $ n - 1) <|> pure []
+
+-- | Apply action between zero and @n@ times, inclusive, and discard results.
+atMost_ :: Alternative f => Int -> f a -> f ()
+atMost_ n action = go n
+    where
+    go n =
+        if n <= 0
+            then pure ()
+            else action *> (go $ n - 1) <|> pure ()
+
+-- | Apply action between one and @n@ times, inclusive, and list the results.
+upTo :: Alternative f => Int -> f a -> f [a]
+upTo n action = liftA2 (:) action $ atMost n action
+
+-- | Apply action between one and @n@ times, inclusive, and discard results.
+upTo_ :: Alternative f => Int -> f a -> f ()
+upTo_ n action = action *> atMost_ n action